1. Field of the Invention
The present invention relates to a tool changer configured to automatically change a tool to be mounted on a spindle of a machine tool.
2. Description of the Related Art
There is known a machine tool with a tool change unit capable of reducing tool change time by rearranging tool storage positions on a tool magazine. Japanese Patent Application Laid-Open No. 5-277866 discloses a machine tool provided with a rearrangement unit for rearranging tools accommodated in the tool magazine, based on the machining order and machining time in a machining program. Japanese Patent Application Laid-Open No. 2009-297867 discloses a method of changing tool arrangement by a tool change unit comprising a main magazine and a sub-magazine and capable of delivering tools between the magazines. In this tool arrangement change method, those tools which are not expected to be moved to the sub-magazine can be designated in advance.
Further, there is known a tool change unit for a machine tool, configured to turn a tool magazine to index a tool and change the tool mounted on a spindle. The tool change unit may be of a known type in which the tool is directly transferred from the tool magazine to the spindle without using a dedicated tool change arm or the like. Since this tool change unit does not require the dedicated tool change arm and a drive unit therefor, its structure can be simplified, so that the costs can be reduced and the reliability can be improved.
FIG. 4 and FIGS. 5A and 5B show an example of a machine tool provided with a rotary-magazine tool change unit. FIG. 5A shows a case where a spindle is in a tool change area and FIG. 5B shows a case where the spindle is in a descending area. A machine tool 21 comprises a tool magazine 24 rotatable relative to a magazine shaft 22 about a pivot axis 23. Further, the tool magazine 24 is provided with radially arranged tool grip portions 25.
In tool change operation, a spindle 27 moves from a machining area to the tool change area, and a tool 28 is delivered from the spindle 27 to that one of the tool grip portions 25 which is located in a tool change position 26. Thereafter, the tool magazine 24 is turned to index that tool grip portion which is mounted with the tool to be used next to the tool change position 26. Then, the tool grip portion indexed to the tool change position 26 delivers the tool to be used next to the spindle 27. The tool mounted on the spindle 27 is changed in this manner.
FIGS. 6A, 6B, 6C and 6D are schematic views showing an example of the operation of the tool magazine during conventional tool change operation. In an operating procedure of this example, tools are changed starting with a tool A having so far been mounted on the tool grip portion of tool number 1 and ending with a tool E mounted on the tool grip portion of tool number 5.
First, the spindle moves from the machining area to the tool change area, whereupon the tool A mounted on the spindle is delivered to the tool grip portion of tool number 1 (FIG. 6A→FIG. 6B).
Then, the tool magazine 24 is turned to index the tool grip portion of tool number 5 mounted with the tool E to the tool change position (FIG. 6B→FIG. 6C).
Thereupon, the tool E is delivered from the tool grip portion of tool number 5 to the spindle 27 (FIG. 6C→FIG. 6D).
FIG. 7 is a flowchart illustrating the operation of a prior art machine tool. The following is a sequential description of steps of processing.
[Step sb01] Tool change is performed (or the tool of tool number 1 is mounted on the spindle).
[Step sb02] Machining by the tool A is performed.
[Step sb03] Tool change is performed. More specifically, the tool A is held by the tool grip portion of tool number 1, and the tool magazine 24 is turned to index the tool grip portion of tool number 5 holding the tool E to the tool change position. Thereupon, the tool E is mounted on the spindle 27.
[Step sb04] Machining by the tool E is performed, whereupon the processing ends.
Japanese Patent Application Laid-Open No. 63-062630 discloses a tool change unit that uses a spindle motor as a drive source in turning a tool magazine. In changing a tool, this tool change unit enables the tool magazine to rotate toward a spindle head during tool change, thereby attaching or detaching the tool to or from a spindle.
As described in the “BACKGROUND OF THE INVENTION”, the known tool change unit is configured to change the tool storage positions on the tool magazine. In the machine tool of this type, the tool change time can be reduced by previously bringing the tool to be used next close to the tool change position.
In the conventional machine tool, however, the tool change unit should be provided with the dedicated rearrangement unit for rearranging the tools and a tool transfer unit capable of temporarily holding the tools. Thus, there is a problem that the mechanism of the tool change unit is so complicated that the costs increase and the reliability is reduced.